The invention relates in general to munitions and in particular to artillery charges that are ignited with a laser.
Modular artillery charges are known, for example, from U.S. Pat. No. 5,747,723 issued on May 5, 1998, which is hereby incorporated by reference. FIG. 1 is a schematic sectional view of a modular artillery charge 10. Charge 10 comprises a generally cylindrical body 12 with a hollow core 14. Propellant 18 is disposed in body 12. A core igniter bag 16 filled with energetic material is disposed in the hollow core 14. The ends 24 of the hollow core 14 are typically enlarged in a conical shape. The enlarged ends 24 hold end igniter bags 20 that are filled with energetic material. The enlarged ends 24 are sealed from the environment by a pair of seals 22. Each seal 22 is usually a piece of thin, transparent, waterproof material, such as Mylar. The seal 22 is attached to the end of body 12 using, for example, an adhesive 26.
The charge 10 is loaded in a gun and ignited by a laser. Because the ends 24 of charge 10 are identical, either end may be used for ignition. The laser beam passes through the seal 22 and ignites the energetic material in end igniter bag 20. The energetic material in end igniter bag 20 then ignites core igniter bag 16, which ignites the propellant 18. However, the ignition process is not without problems. FIG. 2 is an enlarged schematic side view of one end of the charge 10. End igniter bag 20 includes stitches 28. If the stitches 28 of the end igniter bag 20 are misaligned they become drawn too far into the centerline of charge 10. The laser 30 then impinges on the stitches 28 of the end igniter bag 20, resulting in delayed or no ignition of the energetic material in igniter bag 20.
FIG. 3 is an enlarged schematic view of one end of charge 10. In FIG. 3, the offset distance 0 between the seal 22 and the igniter bag 20 is large. The seal 22 and adhesive 26 act as a diffuser for the laser 30 and force the coherent beam to scatter over a very short distance. The diffusion is exacerbated by the red dye that is applied to the exterior of seal 22. If the separation between the seal 22 and the bag 20 is excessive, as in FIG. 3, the laser energy incident on the bag 20 falls below the required threshold and results in cannon misfire. Thus, there is a need for an artillery charge that can be reliably ignited by a laser. It is also desirable to utilize a lower powered laser to ignite the artillery charge.